Supporter Plugin Bug

I had a user yesterday who is a Supporter with a monthly subscription who contacted me saying they lost all their supporter privileges. Checking it out, I saw that their subscription was still active, and the next payment should be applied today (21st).

Digging into the code I see that the plugin only extends privileges for 30.44 days (2629744 seconds) to monthly subscribers. Since it was 31 days between Paypal subscription payments this month, they lost supporter privileges for 13 1/2 hours yesterday, and freaked out when all their plugins disappeared, nag messages started showing, etc.

I understand that the code is designed to count based on a 365 day year, but can you fix this to work properly for the amount of days in a month?

I would just change the number of seconds, but i'm afraid that on the shorter months the extending will start piling up.

Related, I think this line is wrong in the supporter-framework.php file:

if ( $now > $current_expire ) {
$old_expire = $now;
}

should be:
if ( $now > $old_expire ) {
$old_expire = $now;
}